Meso- and Microporous High-Performance PolymersMeso- and Microporous High-Performance Polymers

Mesoporous Poly(benzimidazole)Mesoporous Poly(benzimidazole)

Jens Weber1,2, Markus Antonietti1 and Arne Thomas1

1) Max Planck Institute of Colloids and Interfaces, Department of Colloid Chemistry, Research Campus Golm, D-14424 Potsdam, Germany2) present address: Arrhenius Laboratory, Stockholm University, Dept. of Physical, Inorganic & Structural Chemistry, S-106 91 Stockholm, Sweden

Microporous PolymersMicroporous PolymersSynthesis and Characterization

monomers & DMF

polycondensation(200°C, 400°C)

4M NH4HF

2

etch silica

solvent mediated hard-templating of silica spheres (Ludox HS-40):

structure of cross-linkedPoly(benzimidazole) (PBI)

J. Weber, M. Antonietti, A. Thomas, Macromolecules 2007, 40, 1299

porosity analysed by small-angle x-ray scattering (SAXS), N2-sorption and TEM:

(point collimation)

200 nm

50 nm

surface areas tunable from 0 to 200 m2g-1 (variation of template content), typical pore size: 10-11 nm, porosities up to 37 vol.-%

Proton Conductivity*

J. Weber, M. Antonietti, A. Thomas, Macromolecules 2007, 40, 1299

*) in cooperation with K.-D. Kreuer (MPI Solid State Research, Stuttgart, Germany), J. Weber, K.-D. Kreuer, J. Maier, A. Thomas, Adv. Mater. 2008, 20, 2595

exact loading

excessloading

phosphoric acid loading necessary:● addition of crystalline H3PO4...● excess loading is necessary because of H3PO4 diffusion into the pore walls (formation of benzimidazolium by protonation)

porosity proven by SAXS and Nitrogen sorption

no porosity detectable

influence of porosity(at fixed acid loading and

cross-linking density)

influence of flexibility(at fixed acid loading and

comparable porosities)amount of cross-linker:

proton conductivity enhancementproton conductivity enhancementby nanostructural controlby nanostructural control

of PBI/Hof PBI/H33POPO

44 adducts adducts

(all measurements at zero humidity)

Proton Conductivity*Proton Conductivity*

Nanoreactor - Organocatalysis*

*) cooperation: P. Makowski (MPI Golm) & F. Goettmann (CEA Marcoule, France); P. Makowski, J. Weber, A. Thomas, F. Goettmann, Catal. Commun. 2008, 10, 243

Knoevenagel condensation catalyzed by mesoporous PBI:

benzimidazole units act as base

aldehyde

nucleophile(e.g. malononitriles)

condensationproduct

●benzimidazole has to be non-protonated to be active●nonporous PBI did not show catalytic activity●less activity for ethylcyanoacetates in comparison to malononitriles (low basicity of PBI)

O

H

CN

CN100 %

CN

CN

O

H

COOEt

CN95 %

COOEt

CN

O

H

CN

CN90 %

CN

CN

O

H

COOEt

CN50 %

COOEt

CN

H

O

CN

CN95 %

CN

CN

H

O

COOEt

CN65 %

COOEt

CN

I. Principle and Soluble Microporous PolymersStiff, contorted polymers from predefined building blocks with 90° kinks cannot pack space-efficiently – ultra high, accessible free volume (micropores)(concept introduced by Budd et al. Chem. Comm. 2004, 230)

9,9'-Spirobifluorene is such a building block:can be modified towards di- or tetrafunctional monomers(dicarboxylic acid and derivatives, diamine, tetrabromo,

tetracarboxylic acid, tetraamine...)

J. Weber, O. Su, M. Antonietti, A. Thomas, Macromol. Rapid Commun. 2007, 28, 1871

Poly(amide) 1Poly(amide) 1Mw= 10 kg.mol-1,PDI = 1.9;

soluble only in DMF, NMP, DMAc...SBET= 0 m2g-1 (precipitated from DMF)

Poly(amide) 2Poly(amide) 2Mw= 15 kg.mol-1,PDI=2.7;

soluble in DMF, NMP, DMAc...and THF!no microporosity if precipitated from DMF, but:

SBET= 156 m2g-1 (precipitated from THF)

Poly(imide) 1Poly(imide) 1Mw= 15 kg.mol-1,PDI=2.7;

soluble in DMF, NMP, DMAc...and CHCl3!no microporosity if precipitated from DMAc,

but: SBET= 551 m2g-1 (from CHCl3)

●strong impact of molecular fine structure (flexibility, interactions, see below)● processing (choice of solvent) is important! (metastable states?)

II. Microporous Networkspoly(amide):not microporous(SBET= 50 m2g-1)

poly(imide): microporous(SBET= 982 m2g-1)

●no influence of synthetic pathway (i.e. onset and course of phase separation)●need of a structure directing agent

(polyimide network from tetra- functional biphenyl monomer did not feature microporosity)

N2-sorption pressure dependent SAXS

structural changes occur! structural changes occur! relaxation might be hindered by secondary

interactions (e.g hydrogen bonding for poly(amide)

Understanding this phenomenon allows the anticipation of other potentially microporous networks:

poly(p-phenylene) type network: microporous + fluorescent

(SBET= 450m2g-1, max (emission) = 460 nm)potential hosts for IPNs withcharge transport materials

However, there are still a lot of open questions:How to characterize “soft”, amorphous microporous materials that undergo structural changes ?

(e.g. swelling in liquid nitrogen) Where are the limitations of the concept of intrinsic microporosity? Can we get a better understanding of the acting forces (modeling?)

J. Weber, M. Antonietti, A. Thomas, Macromolecules 2008, 41, 2880; J. Weber, A. Thomas, J. Amer. Chem. Soc. 2008, 130, 6334

*strategy already used: Göltner and Weissenberger, Acta Polym. 1998, 49, 704)

SiO2 monoliths(to be stored in solvent

to avoid cracks)hybrid material

exchange solventwith monomers &

initiator, polymerize

remove silica(NaOH)

(mesoporous)polymer

synthesis of mesoporous polymers by two-step nanocasting*: synthesis of hierarchical porous polymers using a replication process:

open questions regarding mesoporous polymers:

● pores of ~20 nm are stable in glassy poly(styrene) - what about smaller pores (<10 nm) ?

● stability of pores against solvent and pressure?

● glass transition in weakly cross-linked mesoporous polymers?

(compare controversial discussion aboutTg in thin films, entropic arguments, strain etc...)

synthesis of mesoporous, monolithic polymersof varying chemical nature (styrene; various acrylates (MMA, n-Butyl acrylate...) and cross-linking density necessary...

and:and:

Current Work: Pore Stability in Mesoporous PolymersCurrent Work: Pore Stability in Mesoporous Polymers††

†) together with Lennart Bergström, Dept. of Physical, Inorganic & structural Chemistry, Arrhenius Laboratory, Stockholm, Sweden

macro/mesoporoussilica monoliths**

fill mesopores with monomers/initiator

(capillarity),polymerize & etch silica

macro/mesoporouspolymer monoliths

**prepared by P. Vasiliev: P.O. Vasiliev, Z. Shen, R.P. Hodgkins, L. Bergström, Chem. Mater. 2006, 18, 4933)

Acknowledgements: MPI Colloids & Interfaces: Bernd Smarsly, Helmut Schlaad, Regina Rothe, Marlies Gräwert, Ingrid Zenke, Rona Pitschke, Qi Su, Frederic Goettmann, Phillippe Makowski, Pierre Kuhn, Anna Fischer, Michael Bojdys, Chez Briel Kicker Team, ... MPI Solid State Research: K.-D. Kreuer, Annette Fuchs; Philipps-Universität Marburg; Andreas Greiner, Till von Graberg

DVB/Styrenesilica

● macroscopic shape is maintaned● mesopore replication needs optimization

exemplary picture ofa polymer monolith